The System Manual of SOL-20 - History of Computers

PROCESSOR TECHNOLOGY CORPORATION
Sol THEORY OF OPERATION
SECTION VIII
8.1 INTRODUCTION
This section concerns itself with the hardware aspects of the
Sol Terminal Computer T.M. . It specifically deals with the operation of
the power supply and the logic associated with the Sol-PC and keyboard.
Descriptions of software and the operation of the circuitry
contained in the multitude of integrated circuits (IC's) used in the
Sol fall outside the scope of this section. In some cases, references
to other publications or sections in this manual are provided when it
is felt that additional information will contribute to a better understanding
of how Sol operates. Should the reader wish to delve
further into the operation of a specific IC, we suggest that he study
the appropriate data sheet for that IC.
The section begins with an overview of the Sol design. A
block diagram analysis then provides the reader with an understanding
of the relationship between the functional elements of the Sol-PC.
This analysis sets the stage for detailed descriptions of the circuitry
that makes up these elements. The section concludes with a
block diagram analysis and circuit description of the keyboard.
8.2 OVERVIEW
The Sol Terminal Computer T.M. as the name implies, is both a
terminal and computer. It is designed around the S-100 bus structure
used in other 8080 microprocessor-based computers and incorporates
all of the circuitry needed to perform either function. In essence,
Sol combines a central processor unit (CPU) with several S-100 peripheral
modules--memory, keyboard input interface (including the keyboard),
video display output interface plus audio cassette tape,
parallel, and serial input/output (I/O) interfaces. Sol-20 also includes
a five-slot backplane board for adding other memory and I/O
modules that are compatible with the S-100 bus.
An 8080 microprocessor (the CPU) is the "brain" of the Sol.
It controls the functions performed by the other system components,
obtains (fetches) instructions stored in memory (the program), accepts
(inputs) data, manipulates (processes) data according to the
instructions and communicates (outputs) the results to the outside
world through an output port. (For information on 8080 operation,
refer to the "Intel® 8080 Microcomputer Systems User's Manual.")
As shown in the Sol Simplified Block Diagram on Page X-24 in
Section X, data and control signals travel between the CPU and the
rest of the Sol over three buses: 1) a 16-line Address Bus, 2) an
eight-line Bidirectional Data Bus, and 3) a 28-line Control Bus which
is interfaced to the CPU with support logic circuitry. (Note that
the use of a bidirectional data bus permits eight lines to do the
work of 16, eight input and eight output.) These three buses account
for the bulk of the S-100 Bus which connects the Sol to expansion
memory and I/O modules.
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